1. Field of the Invention
The present invention relates to an automatic focusing method, and particularly to a method for focusing by using a pre-flash.
2. Description of Related Art
Nowadays, the technology of digital cameras and digital camcorders is ever-developing, and the conventional disadvantages such as complicated operation and poor portability in the conventional cameras or analogue camcorders are improved. Nearly all the recent digital cameras have built-in auto-focus mode and multiple manual focus modes provided for the users to properly focus the object. Also, without auxiliary focusing system to measure the distance, a conventional digital camera operating in a dark environment or insufficient light in the indoors could easily lose focus when using only the brightness data obtained from the image sensor. Therefore, some newly developed auxiliary focusing systems mounted with, for example, projection focus auxiliary light or even infrared focus function, are introduced. Unfortunately, such high-end digital cameras are rather costly.
An auto-focus complementary device is disclosed to use a red-eye-reduction means as an auxiliary focusing device, and the method thereof is disclosed therewith. As shown in FIG. 1, the method includes the following steps. Firstly, at step S401, a flash module flashes and provides red-eye-reduction function. Next, at step S402, it is determined whether the brightness provided is proper or not. If it is too dark, then set the focus to a predetermined far position, for example, 3 meters away (as shown in step S406). If it is too bright, then move the focus to a predetermined near position, for example, 1 meter away (as shown in step S405). If the brightness is proper, then roughly adjust the focus of the image capturing means according to the focus data captured by the image sensor at step S403. Afterward, capture the estimated focus of the object sequentially to finely adjust the focus as the red-eye-reduction means flashes sequentially at step S404.
Nevertheless, the red-eye-reduction means is only adapted to short-distance shots for facial expression. As to other short-distance shots for, such as pictures or articles, the auto-focusing effect is not obvious, especially those under insufficient indoor light. Furthermore, the brightness sensed by the image sensor is not equal to the brightness sensed by the red-eye-reduction means when it flashes. And whenever the red-eye-reduction means flashes, the auto-focus module would finely adjust the focus, sometimes even up to four or five times, which is time consuming and power wasting.